Figure 4.

Tick molecules involved in Babesia transmission. Schematic diagram representing general stages of Babesia infection and transmission (Zintl et al., 2003; Chauvin et al., 2009; Florin-Christensen and Schnittger, 2009). Tick genes, for which interference with Babesia acquisition and/or transmission have been proved by genetic tests, are shown in rectangles (see text and the Table 3 for their function and references). Pre-gametocytes in red blood cells, taken up within the blood meal, develop in the tick midgut content into matured gametocytes and gametes (ray bodies, Strahlenkörper) with distinctive spine-like projections. They fuse and give raise to the spherical spiked zygotes, which invade midgut cells. Inside the midgut cells, the zygotes transform, undergo meiosis and differentiate into motile prolonged kinetes (ookinetes). The kinetes escape the midgut cells, enter the hemolymph and invade other tick tissues, including ovary (transstadial and transovarial transmission, respectively). Here they undergo asexual reproduction and produce sporokinetes, which further spread the infection inside the tick or newly emerged larvae. During the next feeding, the kinetes that invaded salivary glands undergo a final cycle of multiplication (sporogony) to produce numerous sporozoites, host-invasive stages of the parasite. The sporozoites enter the tick saliva and infect host.